This invention relates to methods and apparatus for severing tubular material and especially relates to such tubular materials, e.g., tubular films, on a mandrel such as might be found in a sausage casing shirring machine.
Numerous methods and apparatus are known for severing or separating tubes into sections. Examples of some of such methods and apparatus may for example be found in U.S. Pat. Nos. 3,817,131; 3,942,221; 3,993,231; 4,052,770; 4,693,149; 4,708,044; 4,885,821; 4,919,025; and 4,941,378. Numerous methods and apparatus have been designed to cut tubing in the absence of a mandrel or rod within the tube. Examples of such patents are U.S. Pat. Nos. 4,708,044; 4,919,025 and 4,941,378 and Soviet Invention Certificate 914,289. When an internal mandrel is present, it has been conventional to pull the tubing apart, especially when the tubing is of a thin film which is capable of being torn. Such methods are undesirable since they do not result in clean cuts, i.e., the cuts are uneven with undesirable hanging tabbed ends or depressions at the edge of the cut. This is true even when the tubing is first partially severed. Examples of such patents are U.S. Pat. Nos. 3,942,221; 3,993,231; 4,052,770 and 4,885,821. In order to avoid such uneven cuts, attempts have been made to completely cut the tubing about a mandrel. In order to accomplish that, a knife is projected into a cutting position and the tubing is rotated about its longitudinal axis, with or without the mandrel also in rotation, until the cut is obtained. Numerous problems have been associated with such an approach. In particular slippage of tubing on the mandrel in either the radial or longitudinal directions can cause uneven or incomplete cuts and in order to make complete cuts, the knife must penetrate the tube which, in the absence of complicated means or methods of avoidance, can cause the knife to score the mandrel. Examples of such severing methods are described in U.S. Pat. Nos. 3,817,131 and 4,693,149, and U.K. Patent Application 2,070,999.
Soviet Inventor's Certificates 235,975 and 897,544 disclose an apparatus which rotates a knife about the radial axis of a tube to be cut. The apparatus, however, has a number of shortcomings. In particular, to permit the knife to penetrate the tubing without damaging the mandrel, a depression is formed in the mandrel to accommodate the point of the knife. Such a depression has the disadvantage of being able to catch, hold and possibly tear tubing passing over the mandrel.